Various hydraulically actuated work supports are known which seek to accomplish plunger clamping in a work support position. One commercial form employs a plurality of cylindrical pins inserted in the configuration of a roller bearing between stationary housing and movable plunger with an auxiliary wedge locking pin forced from the side to crowd between and provide an interference fit relative to the housing and work support plunger.
Another commercial design involves interfitting clutch plates respectively mounted on plunger and fixed housing elements which are hydraulically actuated to frictional engagement with the plunger at work support level.
A third known commercial construction, which comprises the most relevant known prior art, employs a three segment tapered collet closed by a conical ended piston which is hydraulically actuated and spring returned. An included angle of approximately 25.degree. is employed in the conical end taper. The three segment collet is ground to finished dimension in a solid condition to provide a free fit clearance for the plunger size and then split into three segments. The result upon actuation is substantially a three line contact with the plunger as distinguished from a true surface area contact.